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Abstract

Eight controversies are active in the study of macroevolution. These are: 1) the meaning of the term macroevolution, 2) the role of chance, 3) the role of stasis and gradualism, 4) whether significant change is Iimited to speciation events, 5) the environmental conditions where macroevolutionary change occurs, 6) whether Neodarwinian mechanisms are adequate to explain change, 7) the existence and nature of hierarchical evolutìonary processes, and 8) Darwin’s views about all this. After a brief examination of each of these issues we used the extensive data available for 9 species of European and Nearctic cave Pseudosinella to examine the third, fourth and fifth controversies mentioned above. Our conclusions are that while we are unable to demonstrate ongoing directional selection, we have clear evidence that significant adaptive change is not limited to speciation events. It does however appear that the amount of adaptive change is greater in the process of speciation than in between. We also show that there is no evidence for clear periods of stasis in the evolution of these forms. This leads us to a new model of the macroevolutionary process combining features of gradualism and punctuated equilibrium. We also showed that evolutionary change is not associated with unstable environments but rather with more stable ones.